Identification and characterization of toxin-antitoxin system on plasmid pRC18

HARO C; ARISTIMUÑO FICOSECO MC; STEPANENKO T; OLAYA PASSARELL MJ; VIGNOLO GM; RAYA RR

San Miguel de Tucumán

Simposio; XLV Reunión Annual - Sociedad Argentina de Investigación en Bioquímica y Biología Molecular.; 2009

SAIB

A plasmid-borne toxin-antitoxin (TA) system is composed of a stable toxin protein and an unstable antitoxin component and helps in plasmid maintenance by killing of plasmid-free segregants. The lactic acid bacterium Lactobacillus curvatus CRL 705 harbors plasmid pRC18, which is associated with the production of lactocin  Lac705, a two-component bacteriocin. Although several plasmidcuring protocols have been applied to strain CRL705, no pRC18-cured derivative has been yet isolated; in some lactocin Lac705-negative mutants, plasmid pRC18 seems to undergo structural rearrangements and be in low copy-number (i.e., strain Sac7).In this study, we describe the presence of a putative TA module (partitioning locus) on plasmid pRC18, which is organized in a single operon that produces a 92-amino-acids antitoxin (orf4) and a 118-amino-acids toxin (orf3); these proteins belong, respectively, to the superfamilies PhdYeFM and COG3041. Plasmid maintenance functions of the putative TA locus on pRC18 may explain the remarkable stability of this plasmid.